Reservoir systems, such as petroleum reservoirs, typically contain fluids such as water and a mixture of hydrocarbons such as oil and gas. To remove (“produce”) the hydrocarbons from the reservoir, different mechanisms can be utilized such as primary, secondary or tertiary processes. In a primary recovery process, hydrocarbons are displaced from a reservoir through the high natural differential pressure between the reservoir and the bottom-hole pressure within a wellbore. In order to increase the production life of the reservoir, secondary or tertiary recovery processes can be used (“enhanced oil recovery” or EOR). Secondary recovery processes include water or gas well injection, while tertiary methods are based on injecting additional chemical compounds into the well, such as surfactants and polymers, for additional recovery.
For EOR applications, polymers are added as an emulsion or as powders which are then mechanically mixed directly into water. In either emulsion or powder form, the preparation from start to finish takes hours to complete with multiple mixing/holding tanks and/or special equipment. Additionally, the polymer powder cannot be conveniently pumped, and must be safely transported as bulk chemicals.
In the form of polymer emulsions, polymers are suspended as emulsion in a hydrocarbon carrier fluid such as diesel, mineral oil, etc. There are issues with lumping and dispersing the emulsions into water. The emulsions must be mixed in holding tanks for a considerable length of time for hydration to occur. Emulsions leave amounts of carrier oil in the injected solution, which may have an impact on EOR efficiency, particularly in low permeability reservoir. U.S. Pat. No. 8,383,560 discloses a method for dissolving an emulsion to a final polymer concentration of 500 to 3000 ppm for EOR applications in a complex process requiring multi-step mixing under different conditions.
With the use of powders, particularly when the product is used for off-shore platforms (e.g., on a floating production, storage and offloading or FPSO), elaborate powder equipment is required for the handling of very large quantities of powder. Additionally, much time is needed to suspend the polymer powders directly into water, as well as necessary special equipment for the mixing of powders into water. USP2004/008571 discloses an apparatus and method for hydrating particulate polymer, including a pre-wetter, a high-energy mixer, and a blender. USP 2004/0136262 discloses an apparatus and method for wetting powdered material for subsequent distribution of the material in bulk water for EOR applications. USP 2012/0199356 discloses an installation which includes a “polymer slicing unit” for the dissolution of polymer powder for EOR applications.
There is a need for improved polymer compositions/preparations, and methods to prepare/transfer such polymer compositions/preparations for convenient and efficient EOR applications, particularly off-shore EOR.